Cabling Question

[behrendfry]

I am working on a system that has 3 External power leads and 3 External power returns. 15 Vdc is applied evenly over all leads and my question is should the 3 returns be twisted and the 3 powers be twisted and the twist the power and return sets togethor or shouls there be 3 twisted pairs of a power and return seperate?

 

[JimB]

Your description is a bit difficult to understand, but lets see.

You have three items which require 15vdc power and one power source.

You are asking whether:

1 To loom all the +ve wires together, and loom all the -ve wires together in separate looms. So making two looms.

or

2 To loom the +ve and -ve wires together for each piece of equipment. So making three looms.

My answer is 2. I have seen horrendous problems where method 1 is used.
Switch one power supply of a dual redundant pair, and the other one trips.
Switch one Processor Rack (CPU) and is dual redundant partner crashes because the inrush current in the wires for one CPU induces a voltage spike in the wiring for the other rack. (5 volt supplies dipping to 4.5 volts for a few milliseconds.)
An awful system, a real bag of something brown and nasty.

JimB

 

[behrendfry]

This is a I/O connector on a Thermal Sight. The connector used to have a +ve and a -ve twisted togethor. Now the connector has 3 +ve and 3-ve, not sure why they provided 3 on there new system. The spec calls for :

3.3.1.14.8.1 External power. An external power connector shall be provided on all TWS systems which allow an input voltage range that includes voltages between 5.0-12.0 volts DC, measured at the I/O connector input with respect to the External Power Return Signal, to be provided from a conditioned external source to power the TWS. The voltage ripple and noise shall not be greater than 25 mV p-p and voltage spikes shall not exceed 12 volts. Voltage dropouts (to a voltage less than the minimum specified above) shall be less than 1 msec in duration. These values are specified at the I/O connector input. The TWS shall provide reverse polarity protection for the external power input. The external power input shall be isolated from the battery power source to preclude inadvertent charging of the batteries. Power and RTN shall be applied on all pins evenly. For connector information and pin-out arrangement see Appendix D.

I was writing an ICD and had 3 +ve/-ve twisted togethor and I was aked should it be all the +ve and all the -ve loom togethor then loom the 2 sets. I didn't think that it was correct but I have nothing to back my reasoning.